This application claims the priority benefit of Taiwan application serial no. 89118903, filed Sep. 15, 2000.
1. Field of Invention
The present invention relates to liquid crystal display device. More particularly, the present invention relates to a structure of a liquid crystal display.
2. Description of Related Art
Displaying device is very common in the daily life. Especially, a displaying device cannot be absent in a television set or a computer system, where the displaying device is used to display image to the user. In general, if the displaying device is designed by the cathode-ray tube (CRT) manner, it occupies a large space, causing inconvenient use. For example, a notebook cannot be equipped with a CRT display. In these considerations, a panel displaying device with matrix of pixels is successfully developed. The panel displaying device includes, for example, a liquid crystal display (LCD), or a thin film transistor (TFT) liquid crystal display (TFT-LCD).
For a LCD, particularly to a TFT-LCD, the vision quality for images or words may change from different view direction. If the view angle is too large, the vision quality, such as the illumination contrast ratio, is degraded. A wide view technology is always important to improve the vision quality of the TFT LCD, in which a wide view film is the most efficient way in the wide view technology to improve the vision quality. FIG. 1A is a top view, schematically illustrating a relation between the LCD and the view angle. FIG. 1B is a side view, schematically illustrating the relation between the view angle and the LCD in FIG. 1A. A wide view film 110 is put on a LCD device 100. The images on the LCD device can be viewed from a left 50, right 52, up 56, and down 54. The current wide view film 110 allows the image to be viewed by a view angle of 60 degrees, and the contrast ratio (CR) at that angle is about CR=10. The up view angle is about 30 degrees and the lower view angle is about 60 degrees. In this range of view angle, it is still insufficient.
In the LCD, the liquid crystal means a material of which the material structure is between a crystal and a liquid. When the liquid crystal material is applied with an external electric field, the liquid crystal molecules are affected by the electric field and the alignment structure of the liquid crystal molecules are changed. Due to the difference of liquid crystal alignment, the polarization direction of passing light is rotated. By making use of these properties, the liquid crystal material can be used as a displaying device. Since the LCD has various advantages of small weight, small thickness, low driving voltage, small volume, and low power consumption, LCD has wide applications. However, how to improve the vision quality is an essential issue to continuously develop.
The working principle of the LCD is schematically shown in FIG. 2. In FIG. 2, theory of a twisted nematic (TN) LCD is, for example, shown. A liquid crystal layer 108 is confined between a glass plate 106. A polarizing layer 104 is arranged on the outer side of the glass plate 106 at the both sides, but the polarization direction is vertical to each other. For the left situation in FIG. 2, the incident light is polarized into one direction after the light travels the polarizing plate 104. The polarized incident light then enters the liquid crystal layer 108. When the liquid crystal layer 108 is not applied with a bias, the liquid crystal molecules are twisted by 90 degrees from one side to the other side. Since the polarizing plates 104 for the two sides have vertical polarization direction, the incident light can pass the lower polarizing plate 104.
If the liquid crystal layer 108 is applied with bias, such as the right situation in FIG. 2, the liquid crystal molecules is changed to a line structure. In this manner, the polarization direction of the incident light does not change. Due to the lower polarizing plate 104 has the 90 degree shift to the upper polarizing plate 104, the incident light can not pass the lower polarizing plate when the liquid crystal material is applied with bias.
A TFT LCD typically include a TFT matrix to form the image pixel. The TFT""s are formed by semiconductor technology to form a TFT matrix with respect to the desired pixel matrix. By controlling the bias produced by the TFT, the bias of TFT can control the TN LCD to decide whether the light can travel through or not. In the foregoing, the working principle of the TFT LCD is described. If the displaying image is a color image, the color effect can also by achieved by control of the applied bias. These technology is well known by the skilled artisans. No further description is made here.
For a LCD, the upper polarizer and the lower polarizer with polarization directions vertical to each other are necessary. However, when the light travels through the polarizer, an additional phase angle usually produces. This causes an optical leakage, and consequently causes the poor contrast ratio at the wide angle. Since the wide view technology is the essential method for the TFT LCD to have better image quality, the wide view quality is the key factor to decide whether the wide view technology is successful or not.
FIG. 3 is a drawing, schematically illustrating a conventional structure of a LCD. In FIG. 3, a liquid crystal layer 112 is located at the middle. The arrows on the liquid crystal layer 112 is the rubbing direction of a glass substrate, that is, the aligning direction of the liquid crystal molecules. On both sides of the liquid crystal layer 112, each side has a wide view (WV) film 110 and a polarizer 104. The arrow directions on the polarizers 104 are the polarizing directions. As shown in FIG. 3, the polarization directions on the polarizers 104 are vertical to each other. The principle directions of the WV films 110 are also vertical to each other.
As the light travels through the upper polarizer 104, only the light component polarized at 45 degrees can transmit through the upper polarizer 104. Under proper control of bias on the liquid crystal layer 112, polarization of the light is rotated to match to the lower polarizer 104. Then, the light passes. Usually, a polarizer always has additional phase deviation from polarization direction, causing optical leakage, and consequently causing the poor quality of the image.
FIG. 5 also shows a structure of WV device, which is fabricated by a manner known as a TAC less technology. In FIG. 5, the WV structure includes a first adhesion layer 200. On the adhesion layer 200, it sequentially has a WV film 202, a first TAC substrate 204, a second adhesion layer 206, a second TAC substrate 208, a PVS polarization base film 210, a third TAC substrate 212, and a protection film 214. This is a conventional WV structure. There is no a retardation phase plate. The PVA polarization base film 210 can also serve as a polarizer with polarization direction.
The invention provides a structure of LCD, of which a retardation phase plate is included at the front side or back side of the WV film, so as to delay the polarized light transmitting from the polarizer. Thereby, optical leakage is effectively reduced, and the contrast ratio is effectively increased.
The invention provides a structure of LCD, the structure of LCD included a first polarizer with a first polarization direction along a first angle. A first retardation phase plate is located behind the first polarizer. The first retardation phase plate is used to produce a retardation effect. The retardation direction is the same as the first angle. A first WV film is behind the first retardation phase plate. The WV film is operated along a second angle vertical to the first angle. A liquid crystal layer is located behind the WV film 110. The crystal rubbing direction of the liquid crystal layer is along the second direction. A second WV film is behind the liquid crystal layer. The second WV film is operated along the first angle. A second retardation phase plate is located behind the second WV film. The retardation direction of the second retardation phase plate is along the second angle. A second polarizer is located behind the second retardation phase plate. The polarization direction of the second polarizer is along the second angle.
In the foregoing, two retardation phase plates are used. However, in general, only one retardation phase plate is also sufficient. The condition is that the slow axis of the retardation phase plate is parallel the polarization direction of the passing light.
Moreover, the retardation phase plate can also be located between the WV film and the liquid crystal layer instead.
The invention also provide a WV device, which includes a first adhesion plate. A first WV film is located on the first adhesion plate. A first TAC plate is located on the WV film. A second adhesion plate is located on the first TAC plate. A retardation phase plate is located on the second adhesion plate. A PVA polarization base film is located on the retardation phase plate. A second TAC plate is located on the PVA polarization base film. A protection film is located on the second TAC plate.
In the foregoing, the WV device includes a retardation phase plate to replace the TAC plate in the conventional WV device. This can effectively reduce the fabrication cost and the total thickness of the WV device. In addition, the chromatic aberration of light is effectively reduced.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.